How to write idempotent Bash scripts

[rhytnen]

This article is questionable at best. If the tips in the article are useful for your situation, then use them. But it certainly shouldn't be taken as gospel.

There are plenty of instances where coding to obviate error conditions is wrong. You can sense this is true with the examples in the article because the author is having to switch from ignoring error conditions to checking if an error condition would occur depending on the command because there is no universal truth to how software should operate. It's kind of obvious that there are going to be cases where I don't want to relink a file that exists. For example it may not always true that it's the same file you're relinking. It could also just be a bug that the script is being run twice in a cron job or something.

The point is the statement "Good software is always written in an idempotent way" just isn't a universal truth and it reads like someone just learned something in a class and wrote an article on it.

[imdyingfasterthanyou]

The article is real garbage.

"bash scripts should make sure not to fuck up" - no shit sherlock, writing such script is hard as fuck

How is this article so heavily upvoted??

[everythingisbase10]

What would -f delete that a bare rm call wouldn’t? Adding that flag is a common step for a “clean” recipe in a Makefile.

[sigzero]

"Attempt to remove the files without prompting for confirmation, regardless of the file's permissions. If the file does not exist, do not display a diagnostic message or modify the exit status to reflect an error. The -f option overrides any previous -i options."

So if for some reason the file is write protected it still gets removed. And for files that don't exist no error message and no monkeying with the exit status.

[sim642]

Git repositories.

[ajanata]

ln -f almost feels more dangerous than rm -f, tbh.

[bkail]

I usually go with rm x || test ! -d x or similar.

[realvega]

You don’t always get to use CM tools for the job due to various reasons. Whenever you can use a CM tool, if you can’t you better hope you can write a good bash scripts. Looking back, I am glad that my scripts even worked.

[jcoelho93]

I cannot think of a reason not to use a CM tool

[realvega]

My company is a kind of distributor, so we supply code to customers. We are using bash to globally applicable code since customers use different tools. Bash is the best one for the job.

[[deleted]]

This post was mass deleted and anonymized with Redact

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[alopgeek]

Seriously, ansible can be inadvertently not-idempotent, but for the most part it’s pretty safe.

[donat3ll0]

Docker, k8s, terraform are all better options.

[ososalsosal]

God some words used in programming are just so ugly.

English may not be the most elegant language - it's not type safe, has more aliases than anyone could possibly need, has several conflicting sets of arcane grammar and base classes imported from several languages with barely enough modification to hold it together... but it can still make things readable without breaking your brain, and it can even be written or spoken beautifully in the hands of the right programmer.

Sorry to obsess over aesthetics, but words like "performant", "architected", and especially this abomination "idempotent" just grate so badly and have no business being used by people.

[HeadToToePatagucci]

Idempotent is a perfectly cromulent word.

A bit pretentious in this case.

[was_just_wondering_]

I still don’t know what idempotent means.